Circulatory support system

ABSTRACT

A method for providing at least partial bypass of the heart to supplement the pumping function of the heart to thereby enable the surgeon to perform various surgical procedures thereon includes providing a circulatory assist system having a portable extracorporeal axial flow pump with a pump housing, a rotating pumping member disposed in the pump housing and inlet and outlet cannulated tubes respectively connected to inlet and outlet ports of the pump housing, accessing the patient&#39;s left atrium of the heart with the inlet cannulated tube, accessing the aorta with the outlet cannulated tube, actuating the rotating pumping member to draw oxygenated blood from the left atrium of the heart through the lumen of the inlet cannulated tube and into the inlet port of the pump housing whereby the pumping member imparts mechanical energy to the oxygenated blood passing through the pump housing and directs the oxygenated blood through the outlet port and through the lumen of the outlet cannulated tube to be transferred by the aorta to the systemic arteries and permitting the right side of the heart to function whereby oxygen-depleted blood returning through the systemic veins to the right atrium is directed through the right ventricle to the patient&#39;s lungs for oxygenation and subsequent pulmonary circulation.

BACKGROUND

[0001] 1. Technical Field

[0002] The present disclosure relates generally to circulatory supportsystems, and, more particularly, to a circulatory support system toprovide partial or total bypass of the heart. The present disclosure isfurther directed to an axial flow pump and a portablemicroprocessor-based controller each being adapted for use in thecirculatory support system.

[0003] 2. Background of the Related Art

[0004] Mechanical blood pumps are commonly utilized to temporarilysupport or substitute the pumping function of the heart during heartsurgery or during periods of heart failure. The most widely appliedblood pumps include roller pumps and centrifugal pumps. Typically, thesepumps are a component of a cardiopulmonary bypass system (e.g., aheart-lung machine) which includes an oxygenator, a heat exchanger,blood reservoirs and filters, and tubing which transports the blood fromthe patient through the bypass system and back to the patient. Withthese systems, blood is withdrawn from the patient via uptake cannulapositioned within the vena cavae and atria or ventricles of the heartand pumped back into the pulmonary artery and aorta via a returncannula.

[0005] Although the aforedescribed cardiopulmonary bypass systems havebeen generally effective for their intended purposes, these systems aresubject to certain disadvantages which detract from their usefulness. Inparticular, conventional bypass systems are relatively complicated andexpensive to manufacture, expose the blood to a high surface area offoreign materials which may damage the blood, require fullanticoagulation and cooling of the heart, and require considerable setup time and continual management by a skilled technician. These systemsalso require mechanical oxygenation of the blood which can have adverseaffects on the patient.

[0006] U.S. Pat. No. 4,610,656 to Mortensen/Mehealus Partnershipdiscloses a semi-automatic heart-lung substitution system. The Mortensen'656 system includes a roller pump which pumps blood from the patient'sright heart via a venous cannula to a membrane oxygenator connected atthe output of the roller pump. From the oxygenator, the blood flows to acompliance reservoir which is connected to a pulsatile left heart pump.Blood is pumped by the pulsatile left heart pump through a filter andbubble trap and then returned to the patient's arterial system throughan arterial cannula. The Mortensen '656 system, however, is also arelatively complex device including several pumps and an oxygenator and,consequently, requires attendance of skilled technicians for set-up andoperation.

SUMMARY

[0007] Accordingly, the present disclosure is directed to a circulatorysupport system to support the functioning of the heart. In a preferredembodiment, the support system includes an extracorporeal pump memberhaving a pump housing dimensioned for positioning directly on oradjacent to the chest area of a patient and defining inlet and outletports, a rotating member rotatably mounted in the pump housing to impartmechanical energy to blood entering the inlet port and to direct theblood through the outlet port, an inlet cannulated tube connected to theinlet port of the pump housing and having an inlet open end portiondimensioned for insertion within the patient's heart whereby blood isdrawn from the heart through the inlet cannulated tube and directed intothe pump housing, and an outlet cannulated tube connected to the outletport of the pump housing and having an outlet end portion dimensionedfor insertion within a major blood vessel associated with the heartwhereby blood exiting the outlet port of the pump housing is conveyedthrough the outlet cannulated tube into the major blood vessel fortransfer by the arterial system of the patient.

[0008] The support system is particularly contemplated for left heartbypass while the right heart functions to direct blood to the lungs. Itis envisioned that the right heart may be slowed or even stopped whilethe support system is utilized for left heart bypass.

[0009] A method for providing at least partial bypass of the heart tosupplement the pumping function of the heart to thereby enable thesurgeon to perform various surgical procedures thereon is alsodisclosed. The method includes the steps of providing a circulatoryassist system having a portable extracorporeal axial flow pump with apump housing and inlet and outlet ports, a rotating pumping memberdisposed in the pump housing and inlet and outlet cannulated tubesrespectively connected to the inlet and outlet ports of the pumphousing, accessing the patient's left ventricle of the heart with theinlet cannulated tube, accessing the aorta with the outlet cannulatedtube, actuating the rotating pumping member to draw oxygenated bloodfrom the left ventricle of the heart through the lumen of the inletcannulated tube and into the inlet port of the pump housing whereby thepumping member imparts mechanical energy to the oxygenated blood passingthrough the pump housing and directs the oxygenated blood through theoutlet port and through the lumen of the outlet cannulated tube to betransferred by the aorta to the systemic arteries, and permitting bloodreturning through the systemic veins to the right atrium to be directedthrough the right ventricle to the patient's lungs for oxygenation andsubsequent pulmonary circulation. The left ventricle may be accessedthrough the heart wall, mitral valve or aortic valve. In an alternateembodiment, a second circulatory assist system may be utilized tofacilitate the pumping function of the right side of the heart.

[0010] The present disclosure is further directed to a pump to be usedin the circulatory support system. The pump includes a pump housingincluding an inlet end portion defining an inlet port for permittingblood to enter the pump housing and an outlet end portion defining anoutlet port for permitting blood to exit the pump housing. The inlet andoutlet end portions preferably each have central hub portions withstraightener blades extending therefrom for facilitating passage ofblood through the pump housing. A rotatable member is mounted forrotational movement to the central hub portions of the pump housing. Therotatable member includes at least one impeller blade for imparting pumpenergy to blood passing through the pump housing and a magneticallyactuated rotor. A motor stator is disposed in the pump housing and hasat least one stator blade extending from an inner surface thereof. Theone stator blade and the one impeller blade of the rotatable member arecooperatively configured to exert a substantially axial flow pumpingenergy to blood flowing along the blood path. Preferably, the oneimpeller blade and the one stator blade each extend axially andperipherally within the pump housing.

[0011] The present disclosure is further directed to a control unit tobe used in the circulatory support system. In an exemplary embodiment,the control unit includes circuitry for supplying power to the flow pumpto cause the pump to rotate, and circuitry responsive to a pressuresense signal from a pressure transducer located on the inlet side of thepump (e.g., within the atrium), for commanding a reduction in motorspeed to a lower speed when the pressure is determined to be below apredetermined threshold. The control unit preferably also includescircuitry responsive to a bubble sense signal provided by a bubbledetector mounted to one of the cannulas, for generating a bubble alarmand for causing rotation of the pump to cease if the bubble sense signalindicates the presence of an air bubble. The control unit may furtherinclude circuitry responsive to the bubble sense signal indicating thepresence of an air bubble for causing a clamping device mounted to oneof the cannulas to clamp down on the cannula to prevent air fromentering the patient's bloodstream.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Preferred embodiment(s) of the present disclosure are describedherein with reference to the drawings wherein:

[0013]FIG. 1 is a side plan view of the circulatory support system ofthe present disclosure illustrating the portable pump and the pumpinflow and outflow sections;

[0014]FIG. 2A is a perspective view of the portable pump of thecirculatory support system with inflow and outflow sections;

[0015]FIG. 2B is a perspective view of the portable pump;

[0016]FIG. 3 is a perspective view with parts separated of the portablepump;

[0017]FIG. 4 is a perspective view of the portable pump with portionscut away and in cross-section;

[0018]FIG. 5 is a cross-sectional view taken along the lines 5-5 of FIG.2B illustrating the inlet straightener blades of the pump housing;

[0019]FIG. 6 is a perspective view of the impeller and the statorhousing of the portable pump;

[0020]FIG. 7 is an axial view of the stator housing illustrating thearrangement of the stator blades;

[0021]FIG. 8 is a cross-sectional view of the stator housing taken alongthe lines 8-8 of FIG. 7;

[0022]FIG. 9 is a cross-sectional view of the stator housing withmounted impeller;

[0023]FIG. 9A is a cross-sectional view of an alternate portable pump tobe used with the circulatory support system of FIG. 1;

[0024]FIG. 9B is a perspective view of the outer housing components ofthe pump of FIG. 9A;

[0025]FIG. 10 is a view illustrating the system's control unit and usethereof in conjunction with supporting the pumping function of the heartof a patient;

[0026]FIG. 10A is an exploded view of a clamp to be used with thecontrol unit of FIG. 10;

[0027]FIG. 11A is an illustration of an exemplary front panel for acontrol unit controlling operation of the pump;

[0028]FIG. 11B is a perspective view of an exemplary control unitshowing the front portion thereof;

[0029]FIG. 11C is a perspective view of the exemplary control unitshowing the rear portion thereof;

[0030]FIG. 11D is an enlarged illustration of the rear panel shown inFIG. 11C;

[0031]FIG. 12 is a block diagram illustrating the circuit components ofthe control unit and of the pump;

[0032]FIG. 13 is a block diagram of an exemplary Control CPU used withinthe control unit;

[0033]FIGS. 14A and 14B are flow diagrams illustrative of a softwareroutine running within the Control CPU;

[0034]FIG. 15 is a view illustrating one method of application of thecirculatory support system where the inlet cannula accesses the leftventricle of the heart through the mitral valve and the outlet cannulais disposed in the aorta;

[0035]FIG. 16 is a view illustrating an alternate method of applicationof the circulatory support system where the inlet cannula accesses theleft ventricle of the heart through the wall of the heart;

[0036]FIG. 17 is a view illustrating another method of application ofthe circulatory support system where the inlet cannula accesses the leftventricle through the juncture of the pulmonary veins and through themitral valve;

[0037]FIG. 18 is a view illustrating the use of a second circulatorysupport system for assisting the right side of the heart;

[0038]FIGS. 19-20 are views illustrating an alternative percutaneousmethod of application where the inlet cannula accesses the leftventricle through the aortic valve and the outlet cannula accesses thedescending aorta through the femoral artery;

[0039]FIG. 21 is a view illustrating another method of application ofthe circulatory support system where the inlet cannulated tube accessesthe left atrium of the heart and the outlet cannulated tube is disposedin the aorta;

[0040]FIG. 22 is a view illustrating another method of application ofthe circulatory support system where the inlet cannulated tube accessesthe left atrium through the juncture of the pulmonary veins; and

[0041]FIG. 23 is a view illustrating the use of a second circulatorysupport system for assisting the right side of the heart.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0042] Referring now in detail to the drawings where like referencenumerals identify similar or like components throughout the severalviews, FIG. 1 illustrates a preferred embodiment of the circulatorysupport system in accordance with the principles of the presentdisclosure. Particular features of support system 10 are also disclosedin U.S. Provisional Application Nos. 60/028,070, 60/026,656 and60/026,657, each filed Oct. 4, 1996, and each entitled CIRCULATORYSUPPORT SYSTEM, the contents of each being incorporated herein byreference.

[0043] Circulatory support or bypass system 10 is contemplated tosupplement or totally replace the pumping function of the heart duringcardiac surgery and/or during temporary periods of heart failure. Thesystem 10 can also be used during medical emergencies such as trauma,heart attack or heart failure. Circulatory support system 10 isparticularly contemplated for patients in need of partial bypass of theleft side of the heart while oxygenation of the blood may be maintainedwith the patient's own lungs. Support system 10 is advantageouslyarranged to be a portable unit which facilitates handling and reducescost and incorporates a portable control unit discussed in greaterdetail below.

[0044] Referring now to FIGS. 1-4, support system 10 includes an axialflow pump 12 and inlet and outlet sections 14, 16 associated with theaxial flow pump 12. Inlet and outlet sections 14, 16 will be discussedin greater detail below. As best depicted in FIGS. 3-4, axial flow pump12 includes pump housing 18 composed of housing half sections 18 a, 18 bsecured to each other with the use of adhesives, screws or the like.Inlet and outlet connectors 20, 22 are respectively mounted within inletand outlet openings 24, 26 of pump housing 18. As can be seen, the inletand outlet openings 24, 26 are in axial alignment although offsetarrangements are envisioned as well. In a preferred arrangement,cylindrical mounting portions 20 a, 22 a of the respective connectors20, 22 are positioned within sleeve 62 within the inlet and outletopenings 24, 26 of pump housing 18 and retained therein in a mannerdiscussed in detail below. O-ring seals 28, 30 may be utilized toprovide fluid tight seals between connectors 20, 22 and pump housing 18.Connectors 20, 22 respectively connect inlet and outlet cannulated tubes14, 16 to flow pump 12.

[0045] In a preferred embodiment, the length of the pump 10 ranges fromabout 3.0 inches to about 4.5 inches, more preferably, about 3.76inches, and the diameter ranges from about 0.7 inches to about 2.0inches, more preferably, about 1.2 inches. Other dimensions arecontemplated which maintain the functionality and portability of thepump.

[0046] With particular reference to FIG. 4, inlet and outlet connectors20, 22 include central interior hub portions 32, 34 respectively. Hubportion 32 of inlet connector 20 has inlet straightener blades 36 (e.g.,3) extending from the outer surface of the hub 32 to the inner surfaceof the connector 20 as also depicted in the cross-sectional view of FIG.5. Similarly, hub portion. 34 of outlet connector 22 has outletstraightener blades 38 extending from the outer surface of the hub 34 tothe inner surface of the connector 22. Straightener blades 36 provide anaxial flow effect on the blood entering flow pump to facilitate flow ofthe blood through the pump 12 to improve pump efficiency. Similarly,straightener blades 38 provide an axial flow effect on the blood exitingpump 12 to facilitate blood flow through outflow cannulated tube 16 andwithin the circulating system of the patient. However, blades 36, 38 arenot required and may be substituted with one or more support strutswhich have little or no affect on the blood flow and may function tosupport bearings on which the impeller rotates.

[0047] As depicted in FIGS. 14, outlet connector 22 has snap ring 40mounted about its periphery and retained thereon by spring clip 42. Snapring 40 functions to snap onto housing 18 to retain outlet connector 22onto the housing. Similarly, a snap ring (not shown) may be utilized toretain inlet connector 20 on housing 18, or, in the alternative, theconnectors 20, 22 may be mounted to the housing 18 with the use ofadhesives or the like.

[0048] Referring now to FIGS. 3, 4, and 6-9, pump housing 18 includescylindrical stator housing 44 disposed in central portion 46 of the pumphousing 18. Stator housing 44 may include four stator blades 48 attachedto its interior wall. Stator blades 48 extend axially and alsoperipherally within the interior wall of stator housing 44 to define thegenerally serpentine configuration of the blades shown. Stator blades 48provide a general axial flow type effect on the blood passing throughpump housing 18.

[0049] An impeller 50 extends through stator housing 44 and is mountedvia rotating shaft 52 to interior hubs 32,34 of inlet and outletconnectors 20, 22, respectively. It is envisioned that bearings (e.g.,sleeve) may be utilized to mount shaft 52. The bearings are preferablyformed of polyethylene or the like. Impeller 50 has a plurality (e.g.,5) of impeller blades 54. Impeller blades 54 extend axially andcircumferentially about the outer surface of the impeller 38 to providean axial-flow pumping energy to blood entering pump housing. The outersurface of impeller 50 and the inner surface of stator housing 44 definean, annular gap or blood path 56 through which blood passes through pumphousing 18. Impeller 50 has a built-in 2-pole rotor magnet 58 as bestdepicted in FIG. 9. Blood flowing through this gap washes the bearingsat the junction between the rotating and stationary components to coolthe bearings and prevent thrombosis, thus avoiding having to provide aseal. In a preferred method of manufacture, impeller 50 is molded aboutshaft 52.

[0050] With reference again to FIGS. 3-4 and 9, the motor includes amotor stator 60 and rotor magnet 58. Motor stator 60 includeslaminations and windings disposed between a sleeve 62 coaxially mountedabout stator housing 44, and the interior wall of pump housing 18. Motorstator 60 is electrically connected to an external energy source. Stator60 provides the appropriate electromagnetic forces to rotate the rotormagnet 58 and impeller 50. Thus, due to housing 44 and sleeve 62, theblood does not come into contact with motor stator 60. Motor stator 60preferably has an outer diameter of about 0.70 inches to about 2.0inches and preferably about 0.97 inches, thereby keeping the overallsize of pump 10 relatively small.

[0051] Preferably, pump housing 18, stator housing 44 and impeller 50are fabricated from a polymeric material and formed by conventionalinjection molding techniques. In a preferred arrangement all bloodcontacting surfaces are coated with an anti-thrombotic agent to preventthrombosis development.

[0052]FIGS. 9A-9B illustrate an alternate embodiment of the axial flowpump of FIG. 1. In accordance with this embodiment, most of thecomponents including the stator housing 44, impeller 50, etc. aresubstantially similar or identical to the prior embodiment. However,this pump includes an aluminum cylindrical housing 18C which replacespump housing half sections 18 a, 18 b and inlet and outlet end bells 20a, 22 a which are mounted to respective end portions of the pumphousing. End bells 20 a, 22 a support inlet and outlet connectors 20,22. This motor also includes sleeve bearings 55 mounted within hubportions 32, 34 of the connectors 20, 22 to mount shaft 52 forrotational movement. A thrust rod 57 is disposed at least partiallywithin inlet bearing 55 to accommodate thrust loads experienced duringoperation of the pump. Shaft 59 extends the length of impeller 50 anddefines an enlarged tapered section 59 a adjacent the outlet end of thepump.

[0053] With reference again to FIG. 1, inlet and outlet sections 14, 16will be discussed in detail. Each section 14, 16 includes respectiveflexible tubes 66, 68 connected to inlet and outlet connectors 20, 22 ofaxial flow pump 12 by a friction fit. In one illustrative embodiment,tubes 66, 68 preferably extend for a length of about 1-2 feet. Tubes 66,68 may be spring reinforced to facilitate manipulation about theoperative site. Preferably, at least a portion of outlet tube 68 iscompressible for reasons to be appreciated hereinbelow.

[0054] Inlet and outlet cannulas 70, 72 are connected to the remote endsof flexible tubes 66, 68 through respective connectors 74, 76. Inletcannula 70 has a blunt rounded end 78 for insertion into the patient'sheart and a plurality of inflow ports 80 disposed in the side wallsadjacent the blunt rounded end 78 to permit inflow of blood from thechamber of the heart. Outlet cannula 72 has an end 82 defining a bendtherein which facilitates passage through a major vessel, e.g., aorta.End 82 may be straight as well. End 82 defines an outflow port 84(shownin phantom) to permit blood to exit the outflow tube 72 under pressure.Inlet and outlet cannula tubes 70, 72 are also preferably made of aflexible material.

[0055] Connector 74 is a straight connector which retains inlet cannula70 thereon by a friction fit. Connector 76 is a “T” connector havingfemale threaded portion 89 to which is mounted stopcock valve 86.Stopcock valve 86 is a conventional valve having flow control handle 88which rotates through manual manipulation to bleed or remove air fromthe system on the outlet side or section 16 of the system 10.

[0056] The system 10 further includes pressure sensor plug 90 associatedwith inlet section 14. Pressure sensor plug 90 is electrically connectedto cable 92 which extends toward the remote end of inlet cannula 70 topressure transducer 94 mounted to the outer surface of the inlet cannula70. Pressure transducer 94 is utilized to detect pressure within theheart chamber.

[0057] The system 10 also includes pump control plug 96 which connectsto the power source for energizing the pump 12.

[0058] Control Unit

[0059] Referring now to FIG. 10, a preferred control unit for use withthe circulatory support system 10 will be discussed. Control unit 100functions in controlling and monitoring the operation of the assistsystem and for sounding audible alarms for various conditions such asthe presence of air bubbles in the bloodstream, low blood flow rate, andso forth. Control unit 100 is preferably mobile to facilitate hospitaluse. The control unit 100 includes a monitor/control panel 102 whichprovides readouts of blood flow rate and pump speed. Panel 102 includesa large knob 109 to allow an operator to control motor speed and hence,blood flow rate. Panel 102 also includes light emitting diodes, each ofwhich is lit when an associated alarm condition exists. Control buttonson the front panel enable the operator to control various functions suchas re-starting the motor. The control unit also preferably has a reardisplay panel identical to that of the front panel for displaying thesame information, so that the system parameter and alarm information isvisible from the rear as well as from the front of the control unit.

[0060] Blood flow rate is determined with a flowmeter/bubble detectsensor 104 clamped onto inflow tube 66. Sensor 104 shown schematicallyin FIG. 10 may be embodied as a conventional ultrasound flowmeter andbubble sensor packaged as a single unit. Preferably, the electronics areshared between the flow sensing and bubble detection functions tominimize the electronics and size. Generally, flow sensing isaccomplished conventionally by transmitting and receiving ultrasoundsignals diagonally across the cannula in both the upstream anddownstream directions, and comparing the phase of the upstream anddownstream signals to ascertain the flow rate. The bubble detection isbased on a measurement of the amplitude of the received ultrasound waverelative to the transmitted wave. If the amplitude of the receivedsignal suddenly drops below a threshold, then the presence of an airbubble is indicated. Output signals generated by sensor 104 indicativeof the flow rate, and of the presence of air bubbles in the system arerelayed back to controller 100 via dedicated wires within harness 64.Operating voltage to sensor 104 is also provided on the wire harness. Asuitable flowmeter/bubble detect sensor 104 is available commerciallyfrom Transonic Systems Inc., located in Ithica, N.Y., Model No. H9X197.As an alternative, the flow sensor and air bubble detectors may beembodied as separate units.

[0061] A solenoid triggered cannula clamp 118 shown schematically inFIG. 10 is mounted on the output tube 68 of output section 68. Whencontroller 100 determines that the blood stream contains air bubbles,based on the output signals provided by sensor 104, it sends anactuating voltage on harness 64 to the clamp 118 to cause it to clampdown on the output tube 68 to crimp the tube and prevent air fromentering the bloodstream. One suitable clamp is shown in FIG. 10A. Withreference to this Figure, the clamp (shown in exploded view) includeshollow cylinder 1000, left clamp 1002 pivotally mounted to the cylinder1000 about pivot pin 1004 and defining clamping surface 1006, and latchpin 1008 which locks the left clamp 1002 in the open and closed positionby reception within a corresponding opening (not shown) defined in thecylinder. A pair of finger grips 1010 and associated finger grip pins1012 are mounted within respect to left clamp 1002. Finger grips 1010and grip pins 1012 are depressed inwardly to release latch pin 1008 topermit opening of left clamp 1002 to position output tube 68 therein.The clamp further includes right clamp 1014 and retaining bar 1016having distal bore 1018 to receive pin 1020 of right clamp 1014 tofixedly connect the two components. A link mechanism 1022 is mountedtoward the proximal end of retaining bar 1016 and is fixed at itsproximal end to retaining bar 1016 via pin A and at its distal end tostationary support plate 1024 via pin B.

[0062] Support plate 1024 is mounted to the proximal end of cylinder1000 and defines an axial opening to permit reciprocal movement ofretaining bar 1016. A solenoid 1026 is mounted adjacent link mechanism1022 and includes solenoid plunger 1028 which moves upwardly uponactuation to engage link mechanism 1022, more particularly, pin C of thelink mechanism 1022, to actuate the link mechanism to drive retainingbar 1016 distally. The clamp further includes a handle mechanism 1030which resets the link mechanism 1022 to its rest position. In thedrawing, link mechanism 1022 is shown in the actuated position. Prior toactuation, the link mechanism 1022 is in an over toggled position (wherethe links of the linkage mechanism are in linear alignment) with theplunger 1028 resting on pin C. When a bubble is detected, the clamp isactuated which drives solenoid plunger 1028 of the solenoid 1026upwardly, tripping the link mechanism 1022 to the position shown in FIG.10A. During movement to this position, link pin A drives retaining bar1016 and right clamp 1014 distally to thereby clamp tube 68 between leftclamp 1002 and the right clamp 1014. To reset, the handle mechanism 1030is pulled rearwardly. As the retaining bar 1016 is pulled to the right,the linkage mechanism 1022 will again over toggle ready to be tripped bythe solenoid plunger. Another clamp suitable for this use is disclosedin U.S. Pat. No. 4,524,802 to Lawrence, the contents of which areincorporated herein by reference.

[0063] Referring again to FIG. 10, also included within wire harness 64are wires that are routed to pressure sensor plug 90 (FIG. 1) which, inturn, is connected to wire 92 and pressure sensor 94 disposed at thedistal end of inlet cannula 70, typically in proximity to the patient'sheart. (The wires and sensor plug 90 are not shown in FIG. 10 for easeof illustration). These wires carry operating voltage to the pressuresensor 94 from control unit 100. The pressure sensor 94 provides anoutput signal representing the pressure sensed (also referred to hereininterchangeably as “inlet pressure of the pump 12). This output signalis routed to control unit 100 via wire harness “h”. If inlet pressure istoo low, motor speed is reduced to prevent suction occlusion.

[0064] With reference now to FIGS. 11(A-C) and 12, further details ofthe components of control unit 100 will be discussed. As shown in FIG.11A, control panel 102 of the control unit includes LEDs 108 a to 108 iarranged in a “traffic status board” type layout. Push-button switches124-134 are located at the bottom of the panel. A large dial 109 ismanually rotatable to set motor speed. Readouts of measured motor speedin revolutions per minute (RPM) and measured blood flow rate in litersper minute (LPM are digitally displayed directly above the dial.

[0065]FIGS. 11B and 11C show respective front and rear perspective viewsof control unit 100. Unlike conventional hospital equipment, controlunit 100 is embodied in the general shape of a long solid rectangle,with an exemplary height of about 48-50 inches, preferably, 54.5 inches,a width of about 7-12 inches, preferably, 9.7 inches, a thickness ofonly 3-7 inches, preferably, 5.5 inches, and with a suitable basesupport 112, preferably on wheels. Hence, control unit 100 isergonomically designed to occupy a minimal amount of operating roomspace. Also, the height of the display panel 102 relative to the basesupport is high enough to prevent obstruction of the panel by thepatient lying on the adjacent operating table. Base support 112 has sideportions 115 that are approximately flush with the sides 123 of the mainrectangular body of the control unit to conserve space. The front andrear portions of the base support each protrude about six inches fromthe main rectangular body. A handle 113 is provided on the front portionof the solid rectangular body.

[0066] A display panel 103 of preferably the same display format as thefront panel 102 is provided on the rear of control unit 100, so that thealarm LEDs, motor speed and flow rate are visible from the rear as wellas from the front of control unit 100. As such, visibility of theinformation by several personnel is facilitated. The motor speed controldial and push-button switches 124-134 are omitted from the rear display.Display panel 103 is shown in more detail in FIG. 11D.

[0067] Referring to FIG. 12, control unit 100 includes a Control centralprocessor unit (CPU) core 150 which receives input signals from variouscircuit components within the control unit and within pump 12, and, inresponse, provides appropriate output signals to implement a host offunctions. A Display CPU 160 acts as an interface between Control CPUcore 150 and each of the push-button switches 124-132, LEDs 108(a-i) andthe motor speed and flow rate displays. A Main Motor Controller/Driver170 provides the drive power to motor 60 responsive to a pulse widthmodulated (PWM) signal from Control CPU core 150. A back-up MotorController/Driver 180 is provided to control the motor in a manual modeduring emergency situations, for example.

[0068] A simplified block diagram of Control CPU core 150 is presentedin FIG. 13. A processor 202 such as Motorola MC 68332 communicates withthe peripheral components such as Display CPU 160 by means of aUniversal Asynchronous Receiver/Transmitter (UART) 204. Processor 202contains a Time Processor Unit or PWM converter 212 which is used togenerate a PWM signal for application to motor controller/driver 170 tocontrol motor speed. Alternatively, a digital to analog (D/A) convertermay be coupled to processor 202 and would provide an analog outputvoltage to control motor speed responsive to a digital word fromprocessor 202. Control CPU core 150 and Driver CPU 160 are in constantcommunication via UART 204. (Display CPU 160 utilizes a similar UARTtherewithin). Each time Control CPU core 150 sends a “display” message,the Display CPU responds with a “key” message to indicate the status ofthe key presses. Typically this “key” message will indicate that no keyshave been pressed and imply that the previous message was received. Allmessages may contain a checksum such that exclusive-OR of all the bytesresults in 0×00. The Control CPU core and Display CPU may communicateusing standard communications protocols, e.g., at 9600 baud, with evenparity, seven data bits, one stop bit and without handshaking lines.Control CPU 150 also includes SRAM 208, e.g., 256 Kbit or higher, whichmay be used to store measured data as well as for storing parametersduring computations performed by processor 202. Processor 202 alsoretrieves various parameter information such as threshold data stored inoptional EPROM 210 (e.g. 64 Kbit×16) or within flash memory 206.

[0069] In operation, referring again to FIG. 12, depression of AC powerswitch 137 switches AC line voltage to main power supply 172 as well asto back-up power supply 174, each of which rectify the AC to provide DCoutput voltages (e.g. 8-15V DC) for powering the various circuitcomponents of the system. Main power supply 172 also supplies voltage toa battery charger circuit 171 which charges battery 176. A switch 179detects voltage output from main power supply 172 and, if it is within apredetermined voltage range, switches this voltage to output line 187.If switch 179 detects that the voltage output from power supply 172 isout of range, it switches voltage from battery 176 to output line 187.In either case, the voltage output on line 187 is provided to apush-button controlled relay 134. Likewise, switch 181 detects voltagefrom back-up power supply 174, and if this voltage is within thepredetermined range, it switches the voltage to its output line 183.Otherwise, switch 181 switches the battery voltage from battery 176 toits output line 183. Switches 179 and 181 are preferably diode switches.

[0070] When relay 134 is activated, the DC voltages on lines 183 and 187are switched to respective output lines 203 and 207. The voltage onthese lines are provided as main power to CPU core 150 and CPU 160 andother circuit components of control unit 100. Each circuit componentreceiving main power will utilize the operating voltage from either line207 or 203.

[0071] Isolation power supply 190 includes a DC to DC converter toconvert the voltage on line 207 (if present) to a higher voltage (e.g.,24V DC) to provide isolated power. The purpose of the isolated power isto diminish the possibility of electric shock to the patient undergoingtreatment. As such, the isolated power is supplied to the circuitcomponents which are directly coupled to sensors which may contact thepatient or the patient's blood. Hence, isolated power is supplied toMotor Controller/Driver 170, pressure transducer 94, flow 5 rate/bubblesensor 104, cannula clamp 118, and optional motor speed sensor 61. Themain power at the output of switch 134 is supplied to the remainingcircuit components of the control unit.

[0072] When relay 134 is activated, output voltage on line 203 is alsoprovided to back-up isolation power supply 182, which provides back-upisolation power to back-up Motor Controller/Driver 180 and to the engageback-up switch 132.

[0073] A multi-channel A/D converter 111 (e.g., eight channels) iscoupled to the battery 176 and to output lines 203 and 207, and convertsthe respective voltages at those points to digital output signals whichare supplied to CPU core 150. From the digital signal associated withthe battery, CPU core 150 determines whether the battery voltage isbelow a predetermined threshold. If so, it commands Display CPU 160 tolight the “Low Battery” LED on the display. CPU core 150 also determinesfrom the digital outputs whether the battery is in use. If it is, CPUcore 150 provides a corresponding alarm command to CPU 160, which thencauses the “Battery in Use” LED 108 i to light.

[0074] A/D Converter 111 is also coupled to motor speed dial 109 andprovides CPU core 150 with a digital output indicative of the dialposition. In response, CPU core 150 outputs a PWM signal S_(C) (producedby the PWM converter therein) to Motor Controller/Driver 170 throughopto-coupler array 175. This opto-coupler array is used for isolationpurposes to prevent voltages from within CPU core 150 from accidentallycausing electric shock to the patient. Other isolation techniques suchas transformer-coupled isolation may alternatively be used. MotorController/Driver 170 includes processing and drive circuitry to varythe drive voltage provided to motor 60 on leads 64 a responsive to thePWM of signal S_(C), in order to control motor speed and starting orstopping of the motor.

[0075] If the “engage back-up” switch 132 is depressed, then Back-upMotor Controller/Driver 180 is utilized to drive the motor 60. TheBack-up Controller/Driver 180 does not receive motor control signalsfrom CPU core 150, but rather, it is directly coupled to the motor speeddial 109 and controls motor speed in accordance with the dial position.Switch 132 switches the voltage output from the appropriateController/Driver 170 or 180 to motor 60 via lines 64 a. Thus, the“engage back-up” switch 132 is utilized when the operator desires tooverride the automatic control by the CPU core such that the motor speedis controlled manually. This manual operating mode is useful inemergency situations when the control unit cannot properly control bloodflow under CPU core control.

[0076] A feedback EMF signal from the motor coils is provided back toboth Controller/Driver 170 on line 64 b and to Controller/Driver 180.The processor within Controller/Driver 170 or 180 determines the actualmotor speed based on the feedback EMF signal, compares the actual speedwith the desired speed according to signal S_(C) (or according to thedial 109 position directly when the back-up Controller/Driver 180 is inoperation), and adjusts the drive voltage provided on lines 64 a toobtain the desired speed within a predetermined tolerance. The actualmeasured motor speed is continually or periodically communicated byController/Driver 170 to the Control CPU core 150 as signal S_(F).Control CPU core 150 in turn transmits the motor speed information toDisplay CPU 160 to display the same on control panel 102.

[0077] Both Controller/Drivers 170, 180 include a current limitingcircuit which limits current drawn by motor 60 to a predeterminedmaximum. If the maximum current is reached, this is indicative of themotor 60 or pump 12 malfunctioning. When maximum current is reached,Motor Controller/Driver 170 forwards a signal S_(i) back to the ControlCPU core 150 indicative of this condition. CPU core 150 responds bysending a message to Display CPU 160 to light the “pump” LED 108 _(d)and sound an audible alarm. However, this condition does not stop themotor. (The Back-up Controller/Driver 180 may also be designed tocommunicate this information back to CPU core 150).

[0078] Suitable controller chips which may be utilized withinController/Drivers 170 and 180 to perform many of the above-describedfunctions are commercially available from several manufacturers.Examples include U.S. Philips Corporation, located in Sunnyvale, Calif.(part No. Philips TDA-5140) or from Micro Linear Corporation, San Jose,Calif. (part No. Micro Linear 4425). Both of these controller chipsoperate as sensorless controllers which monitor the feed-back EMF fromthe motor coils to determine and control the motor speed. As analternative, a controller used in conjunction with a motor speed sensor61, e.g. a Hall effect sensor, could be employed. In this embodiment,feed-back EMF would not be used. Sensor 61 is positioned adjacent motor60 and provides a signal S_(M) indicative of the sensed motor speed online 64 c. This signal is routed to Motor Controller/Drive 170 (or 180)which derives the measured motor speed from the signal and then adjuststhe voltage drive or pulse width modulation (PWM) signal-to the motoraccordingly to adjust motor speed. Signal S_(M) is also provided toControl CPU 150 through opto-coupler 191 to enable the instantaneousmotor speed to be displayed on the display panel as in the case above.

[0079] Attention is now turned to flow rate/bubble sensor 104. Asdiscussed above, this sensor provides measurement of blood flow rate andmonitors for bubbles in the blood, preferably using ultrasound. Theexistence of any bubbles greater than a predetermined size can cause aserious medical condition since air is being pumped into thebloodstream. Hence it is desirable for the operator/surgeon to beimmediately apprised of a bubble condition whereupon it can beeffectively remedied as soon as possible. In accordance with the presentdisclosure, if a bubble condition is sensed, the pump is immediatelycaused to shut down to allow the surgeon to instantly remedy the bubblecondition such as by sucking out the bubble with a syringe. Followingmotor shut-down due to a bubble condition, the motor does not startagain automatically, but must be manually restarted by depressing therestart pump button 130. In addition, immediately upon the detection ofa bubble condition, control unit 100 sends a command to a clamp controlcircuit 222, which responds by providing an actuation voltage to thecannula clamp 118. The actuation voltage causes clamp 118 to clamp downon the output tube 68, thereby crimping the cannula or tube andpreventing air bubbles from entering the patient's bloodstream.

[0080] In operation, operating voltage is supplied to flow/bubble sensor104 on line 64 f. Sensor 104 outputs a flow rate signal S_(FR) and abubble sense signal S_(B) on lines 64 e corresponding to the associatedconditions within inlet cannula 14. The sensor output signals aresupplied to Flow Rate/Bubble Detect Circuit 140, e.g., a circuit boardproduct available from Transonic Systems Inc., model T109 circuit board.Circuit 140 communicates the sensor output signals S_(B) and S_(FR) toControl CPU 150 in a suitable format, and also provides control signalsto sensor 104 to control its operation.

[0081] If signal S_(B) indicates the presence of a bubble condition,Control CPU 150 immediately changes the voltage level of motor controlsignal S_(C) (or transmits another signal) to command a shut-down ofmotor 60, whereby Motor Controller/Driver 170 causes motor 60 to ceaserotation. Contemporaneously, Control CPU 150 sends a command signal toclamp control circuit 222 to initiate clamping by clamp 118 by providinga momentary actuation voltage thereto. An alarm signal is sent toDisplay CPU 160 which causes the “Bubble” LED 108 b and the “re-startpump” LED 136 to light or blink. In addition, CPU 150 activates audiblealarm circuit 184 by outputting a tone signal ST and a volume signal SV.The tone signal enables circuit 184 to produce audible output throughspeaker 164. The volume signal causes the audible output to be ramped upto avoid startling the surgeons/nurses. (It is noted here that theaudible alarm circuit 184 is automatically activated by CPU 150 wheneverany of the other alarm LEDs 108 a-108 i are lit. The “silence alarm”button 128 enables an operator to silence the audible alarm each time itoccurs for any of the alarm conditions).

[0082] When the motor is shut down in correspondence with the bubblealarm, the operator may attempt to remove the bubbles from the cannulasuch as by sucking them out with a syringe. Thereafter, to restart thepump, the operator manually resets the cannula clamp, and depresses theRestart pump button 130, which causes the bubble alarm to beextinguished and the motor to be re-started to a speed in accordancewith the manual dial 109.

[0083] In an alternative embodiment, the cannula clamp 118 and theassociated clamp control circuit 222 are eliminated. In this case, abubble alarm condition will still stop the motor as described above topermit the bubble condition to be remedied such as with a syringe. Themotor will then be re-started only after the Re-start pump button 130 ismanually activated.

[0084] The flow rate signal S_(FR) outputted by sensor 104 is routed toCPU 150 in suitable format by detect circuit 140. CPU 150 routes theflow rate information to Display CPU 160 which causes it to be displayedon the panel 102. Control CPU 150 performs a software routine whereinthe flow rate is compared to a threshold value “L1” stored in memorywithin the CPU. If the flow rate drops below “L1” for a predefined timeperiod, e.g., below 2 LPM for more than one second, CPU 150 communicatesa message to CPU 160 to light the “Low Flow” alarm LED 108 e and soundan audible alarm.

[0085] Optionally, control unit 100 also monitors for flow blockage andgenerates a flow blockage alarm via a dedicated LED (not shown) andaudio alarm if blockage is detected. In this case, CPU 150 stores flowrate data continuously and evaluates whether the flow rate has droppedunexpectedly in the absence of the speed dial 109 being moved (after theflow rate having been above a predetermined threshold such as one LPM).If the flow rate drops by a predetermined amount or percent, e.g., bymore than 30% in less than two seconds, then the flow blockage alarm isactivated. The flow blockage alarm is extinguished when the flow raterises above a threshold, e.g., above one LPM.

[0086] Control unit 100 also communicates with pressure transducer 94 toascertain the measured pressure in the transducer's location, e.g., inproximity to or within the atrium, or alternatively, within the inletcannula in a position closer to pump 12. Pressure transducer 94 may be aconventional miniaturized transducer available commercially, e.g., fromOhmida Medical Devices, located in Madison, Wis. Alternatively,transducer 94 is embodied within a housing clamped to the outer surfaceof the inlet cannula, e.g., in proximity to the pump. Pressuretransducer 94 receives operating voltage via leads 64 d (which runwithin the outer sheathing of inlet cannula 14) and outputs a signal SPindicative of the pressure back to the control unit on another one ofleads 64 d. This signal is digitized and received by opto-coupler 197and routed through interface circuit 193 to CPU 150 in suitable format.CPU 150 includes a software routine that stores measured pressure dataand determines whether the instantaneous pressure has dropped below apredetermined threshold “P1”, e.g., to less than 2 mm of mercury. If so,a message is outputted to CPU 160 to light the Low Inlet Pressure LED108 f. Contemporaneously, CPU 150 sends a command to MotorController/Driver 170 to automatically reduce the motor speed at apredetermined rate of reduction, in an attempt to automatically bringthe pressure back. Motor speed continues to drop until the pressurerises above P1 (or above a higher threshold) for more than apredetermined time period, e.g., for more than 1.2 seconds. When thiscondition is satisfied, motor speed is then ramped up to a speed inaccordance with the speed dial 109. (As an alternative, the motor speedis reduced to a predetermined speed, or by a predetermined amount, andis maintained at that lower speed until the pressure rises above athreshold, which is followed by motor speed ramp-up).

[0087] It is noted that control unit 100 may include means to manuallycalibrate or “zero” the pressure measurement. That is, when CPU 150detects that the “Set Zero Pressure” push-button 124 on the panel isdepressed, it reads the instantaneous value of pressure as outputted bytransducer 94 and stores that value as the offset to be used wheneverthe pressure transducer is read. The pressure transducer is preferablyzeroed in this manner by the operator each time the control unit isturned on and prior to the cannulas 14, 16 being attached to thepatient.

[0088] Control unit 100 preferably includes a test mode to verify properoperation of the motor. The test mode is activated by depression of“Test” push-button 126 on the panel, whereupon CPU 150 will send acommand to Motor Controller/Driver 170 to force motor 60 to run for,e.g. 10-15 seconds at varying speeds. In the test mode, the motor willrun regardless of any alarm conditions. The alarm LEDs will still light,but the alarms will not be audible or prevent the motor from runningduring the test mode.

[0089] In addition, a Power On Self-test feature is provided whereby thecontrol unit undergoes a self-test under the control of CPU 150 wheneverpower is S initially turned on. If the CPU detects any error withinitself or any of its peripherals, CPU 150 will not allow the unit torun. The self test preferably includes a RAM test to determine if theRAM is accessible and a ROM test to ascertain that the check sum of thecode has not changed. A test for invalid readings from any sensor isalso included, as well as a connectivity/continuity test and a displaytest. If there are any errors, the LED on the front panel correspondingto the faulty circuit component will be lit and all dashes displayed onthe flow rate and motor speed displays. If there are no errors, none ofthe LEDs will be lit and all zeroes are preferably displayed on the flowrate and motor speed displays.

[0090] During system operation, checks are continually performed onvarious components to verify proper continuity and operation, and analarm is generated if a fault is detected. For instance, the “flowsensor” LED 108 c on the front panel is lit and an audible alarm issounded if the flow sensor 104 is determined to be electricallydisconnected from control unit 100, or if the bubble amplitude readingsare below a predetermined threshold, indicating improper mounting orcontact between the flow sensor and the tubing. The clamp controlcircuit 222 continually samples the continuity of the cannula clamp 118,and reports faults to the CPU 150. The “clamp” LED 108 a is lit and analarm sounded if continuity is deemed inadequate. The “electronics” LED108 g is lit and a buzzer activated if the control CPU 150 is notreceiving adequate messages from the display CPU 160, or if any powersupply voltages are out of specification. The control unit 100 alsoincludes a connector (not shown) within the unit housing to enableconnection to a personal computer (PC) to aid in the testing of thecontrol unit. Communication with the PC may be transferred at, e.g.,9600 baud with no parity, eight data bits, one stop bit and withouthandshaking lines.

[0091] Referring now to FIGS. 14A and 14B, a simplified flow diagramillustrating operation of a software routine running on Control CPU core150 is presented. Upon manual activation of the power switches (step302) the Control CPU 150 performs the above-described self-test (step307). If any errors are detected in step 308 the motor is disabled (step309), the LED 108 on the panel associated with the faulty component willbe lit (step 310) and the unit will be non-functional until the problemis corrected. Also, the motor speed and flow rate displays will show alldashes (step 311). If no errors are detected, the CPU core thendetermines in step 312 if the battery is in use or the battery is low,based on the digital outputs from A/D converter 111. If either conditionis present, the corresponding LED is activated in step 313 by means of acommand sent to Display CPU 160.

[0092] Next, CPU 150 determines the speed dial position in step 314based on the output of converter 111, and forwards control signal S_(C)to Motor Controller/Driver 170 to run the motor at the desired speed.With the motor running, bubble sense signal S_(B), flow rate signalS_(FR), pressure sense signal S_(P) motor speed sense signal S_(M) (orS_(F)) and current limit signal Si are transmitted to CPU 150 by therespective circuit components as discussed above (step 316). Thesesignals may be received by the UART within CPU 150 and stored in theSRAM and/or flash memory. The motor speed and flow rate are determinedbased on S_(M) (or S_(F)) and S_(FR), respectively, and commands aresent to the Display CPU to display the same on the display panel. TheControl CPU then evaluates the bubble signal S_(B) (step 318). If abubble is determined to be present, the motor is shut down and thebubble alarm activated (step 320). At this point the CPU core detectswhether or not the Re-start button has been pressed in step 322. When itis depressed, the bubble alarm is de-activated (step 323) and thesoftware flow returns to step 314 where the motor is started again.

[0093] If in step 318 there is no bubble detected greater than apredetermined size, the next step is to ascertain whether the blood flowrate is less than the threshold level L1 (step 324). If so, the low flowrate alarm is activated in step 326. The alarm remains activated unlessthe flow rate rises above a threshold L2, e.g., 10% higher than L1(steps 327, 329). The low flow rate condition does not stop the motor.

[0094] Next, in step 340 (FIG. 14B) the CPU core evaluates whether theinlet pressure has dropped below the threshold P1 (in mm Hg). If it has,the low inlet pressure alarm is activated (step 342) and the motor speedis automatically reduced in step 344. The motor speed reduction iscarried out at a predetermined rate of reduction. If the inlet pressureis still below P1 in step 345, then the flow is returns to step 344where the motor speed is reduced further. The motor speed isincrementally ramped down in this manner until the inlet pressure risesabove P1. When it does rise above P1, the motor speed is maintained atthe latest reduced speed in step 346. Then, in step 347, if the inletpressure is above P1 for a specified time interval, e.g. for 1.2seconds, the motor speed is ramped up in step 20 349. Otherwise, theflow returns to step 345. Once the motor speed is ramped up in step 349to a speed in accordance with the motor speed dial 109, the pressurealarm is de-activated in step 350 and the flow returns to step 370.

[0095] The next step (step 370) is to determine if the motor current isat the limit, based on the signal Si provided by the MotorController/Driver 170 or 180. 25 If the limit is reached, the Pump alarmis turned on in step 375, otherwise, it is commanded off in step 380.The software flow then returns to step 312 where the diagnostic routineis repeated.

[0096] Preferred Arrangements for Connecting the Support System

[0097] Preferred arrangements for connecting the support system 10 willnow be discussed. With reference again to FIG. 10, support system 10 isillustrated for use with an open (full medial) sternotomy which involvesthe splitting of the sternum bone to gain access to the heart. Asdiscussed above, support system 10 is contemplated for use in assistingthe left side of the heart while the blood flows through the right sideto deliver blood to the lungs for oxygenation. As depicted, flow pump 12of support system 10 is sufficiently small to be placed directly on theupper chest of the patient away from the sternal area and may be securedto the chest with conventional medical tape or secured to the drape withconventional surgical clips. Inflow and outflow sections 14, 16 are thenappropriately positioned adjacent the chest cavity to access the heartand/or major blood vessels. With reference now to FIG. 15, onearrangement for connecting the system is described. Inlet cannula 70 ofinlet section 14 is introduced through the heart wall and passed throughthe mitral valve “MV” with the inflow ports 80 positioned in the leftventricle “LV” as shown. Outlet cannula 72 is inserted through the aortawall with the use of end portion 82 with the outflow port 84 positionedin a downstream position within the aorta “A”. Upon operation of thesystem 10, blood is withdrawn from the left ventricle “LV” throughinflow ports 80 of inflow cannula 70 and directed to the pump 12. Pump12 imparts mechanical pumping energy to the blood and directs the bloodunder pressure through outflow cannula 72 and into the aorta “A”, thusassisting the functioning of the left side of the heart. The blood iscirculated throughout the body via the body's circulatory system andthrough the right side of the heart to the patient's lungs foroxygenation. During operation, monitoring, checking and controlling thesystem 10 is performed with control unit 100 to calculate flow rate,pressure within the heart, air bubble detection, etc. . . . as discussedhereinabove.

[0098]FIG. 16 illustrates an alternate method whereby the inflow cannula70 accesses the “LV” through an incision formed in the wall of theheart.

[0099]FIG. 17 illustrates another alternate method of application ofcirculatory support system 10. In accordance with this method ofapplication, 5 inflow cannula 70 is introduced into the left ventricle“LV” through the region adjacent the juncture of the pulmonary veins“PV” (left or right) and passed through the mitral valve “MV” with theinflow ports 80 of the tube 70 located within the left ventricle “LV”.

[0100]FIG. 18 illustrates an alternate method of application where twosupport systems are used for total heart bypass. The support systemutilized for bypass of the left side of the heart is identical to thatdescribed in connection with FIG. 15. The support system utilized forright heart bypass has its inflow cannula 70 inserted through the heartwall with the inflow ports 80 positioned in the right ventricle “RV”.The outflow cannula 72 is positioned in the pulmonary aorta “PA” indownstream orientation as shown. In this application, the lungs arestill utilized to oxygenate the blood.

[0101]FIGS. 19-20 illustrate yet another method of application of thecirculatory support system. In accordance with this percutaneousapproach, inflow cannula 70 is percutaneously inserted throughsubclavian artery to the aorta “A” and advanced through the aortic valve“AV” with the inflow ports 80 of the tube 14 positioned within the leftventricle “LV”. Inflow cannula 70 has expandable membrane 98 (e.g., aballoon) positioned about its periphery to occlude the aorta “A”. Asecond catheter 99 (as shown) may be coaxially mounted about the cannula70 to provide the inflation fluids to expand membrane 98 as isconventional in the art. The second catheter may include a connector 99a, e.g. a Luer connector, for providing the inflation fluids to bepassed to membrane 98. It is also envisioned that inflow catheter 14 mayhave a separate lumen extending therethrough and terminating in a port99 b and port 99 c to permit the introduction of cardioplegia solutionwithin the heart to temporarily discontinue the pumping function of theheart, and/or for venting the left ventricle. Outflow cannula 70 isinserted, preferably, percutaneously within the femoral artery andadvanced into the descending aorta “a”.

[0102] In application, flexible membrane 98 is expanded to isolate theleft side of the heart. The support system 10 is actuated to draw bloodfrom the left ventricle “LV” through inflow ports 80 and into inflowcannula 70. The blood is directed through inflow cannula 70 and issubjected to the pumping energy of portable pump 12. The blood isreturned through tube 68 and outflow cannula 72 and into the descendingaorta “a”. During use, cardioplegia fluid or venting capabilities may beintroduced via inflow catheter tube 14 and port 99 b to be depositedfrom port 99 c as described above.

[0103] With reference now to FIG. 21, another arrangement for connectingthe system is described. Inlet cannulated tube 14 is introduced throughthe heart wall with the inflow ports 80 positioned in the left atrium“LA” as shown. Outlet cannula 72 is inserted through the aorta wall withthe use of end portion 82 with the outflow port 84 positioned in adownstream position within the aorta “A”. Upon operation of the system10, blood is withdrawn from the left atrium “LA” through inflow ports 80of inflow cannula 70 and directed to the pump 12. Pump 12 impartsmechanical pumping energy to the blood and directs the blood underpressure through outflow cannula 72 and into the aorta “A”, thusassisting the functioning of the left side of the heart. The blood iscirculated throughout the body via the body's circulatory system throughthe right side of the heart to the patient's lungs for oxygenation.

[0104]FIG. 22 illustrates another alternate method of application ofcirculatory support system 10. In accordance with this method ofapplication, inflow cannula 70 is introduced into the left atrium “LA”through the region of the juncture of the pulmonary veins “PV” with theinflow ports 80 of the cannula 70 located within the left atrium “LA”.

[0105]FIG. 23 illustrates an alternate method of application where twosupport systems are used for total heart bypass. The support systemutilized for bypass of the left side of the heart is identical to thatdescribed in connection with FIG. 21. The support system utilized forright heart bypass has its inflow cannula 70 inserted through the heartwall with the inflow ports 80 positioned in the right atrium “RA”. Theoutflow cannula 72 is positioned in the pulmonary aorta “PA” indownstream orientation as shown. In this application, the lungs arestill utilized to oxygenate the blood. Alternatively, right bypass canbe effectuated by accessing the right ventricle with inflow cannula 70or left bypass can be effectuated by accessing the left ventricle withany of the arrangements described above.

[0106] Thus, the circulatory support system 10 of the present disclosureprovides for temporary short term heart support (either partial, e.g.,left heart assist, or full support) of a, patient. Set-up and managementof the system requires relatively minimal effort. The entire system 10,i.e., the pump 12 including the motor 60 and associated tubing, can bemanufactured cost effectively to be disposable. The features of thecontrol unit, including the bubble detection, flow rate detection,automatic motor shutdown and clamping of the outlet cannula in case ofdetected bubble, various visible and audible alarms, and so forth, areparticularly tailored to address the needs of an axial flow pump system.The control unit is also ergonomically designed to occupy a small amountof operating room space and to facilitate use in the operating room.

[0107] While the above description contains many specifics, thesespecifics should not be construed as limitations on the scope of thedisclosure, but merely as exemplifications of preferred embodimentsthereof. For example, one or two of the aforedescribed pumps can beplaced in other locations of the body, via other access areas, inaddition to those described above. Also, the pump(s) can be utilizedduring the “window” approach to bypass surgery as well as duringminimally invasive bypass surgery. Those skilled in the art willenvision many other possible variations that are within the scope andspirit of the disclosure as defined by the claims appended hereto.

What is claimed is:
 1. A circulatory support device to supplement thepumping function of the heart to thereby enable the surgeon to performvarious surgical procedures thereon, which comprises: an extracorporealportable axial flow pump including a pump housing dimensioned forpositioning directly on or adjacent to the chest area of a patient, andhaving inlet and outlet ports in substantial axial alignment, a rotatingmember rotatably mounted in the pump housing to impart mechanical energyto blood entering the inlet port and to direct the blood through theoutlet port; an inlet tube connected to the inlet port of the pumphousing and having an inlet open end portion dimensioned for insertionwithin the patient's heart whereby blood is drawn from the heart througha lumen of the inlet tube and directed into the pump housing; and anoutlet tube connected to the outlet port of the pump housing and havingan outlet end portion dimensioned for insertion within a major bloodvessel associated with the heart whereby blood exiting the outlet portof the pump housing is conveyed through a lumen of the outlet tube intoa major blood vessel for transfer by the arterial system of the patient.2. A method for providing at least partial bypass of the heart tosupplement the pumping function of the heart to thereby enable thesurgeon to perform various surgical procedures thereon, the heart havinga left atrium for receiving oxygenated blood from the lungs and a leftventricle for pumping the oxygenated blood through the aorta to thesystemic arteries, and a right atrium for receiving oxygen-depletedblood from the systemic veins and for directing the oxygen-depletedblood through the pulmonary artery and into the lungs for oxygenation,the method comprising the steps of: providing a circulatory assistsystem including a portable extracorporeal axial flow pump having a pumphousing defining a longitudinal axis, the pump housing having an inletport and an outlet port, a rotating pumping member disposed in the pumphousing, an inlet tube having a first end connected to the inlet portand a second end for contact with the body, an outlet tube having afirst end connected to the outlet port and a second end for contact withthe body, each tube having an axial lumen between the first and secondends defining a blood flow path for conveyance of blood therealong;accessing the left ventricle of the heart with the inlet tube such thatthe second end of the inlet tube is in fluid communication with the leftventricle; accessing the aorta with the outlet tube such that the secondend of the outlet tube is in fluid communication with the aorta;actuating the rotating pumping member to draw oxygenated blood from theleft ventricle of the heart through the second end of the inlet tube andthrough the axial lumen of the inlet tube and into the inlet port of thepump housing whereby the pumping member imparts mechanical energy to theoxygenated blood passing through the pump housing and directs theoxygenated blood through the outlet port and through the axial lumen ofthe outlet tube and the second end of the outlet tube to be transferredby the aorta to the systemic arteries; and permitting the right side ofthe heart to function whereby oxygen-depleted blood returning throughthe systemic veins to the right atrium is directed through the rightventricle to the patient's lungs for oxygenation and subsequentpulmonary circulation.
 3. The method according to claim 2 furtherincluding the step of positioning the portable pump either on thepatient's body or directly adjacent the patient's body.
 4. The methodaccording to claim 2 wherein the step of accessing the left ventricleincludes inserting the second end of the inlet tube through the mitralvalve.
 5. The method according to claim 4 wherein the step of accessingthe left ventricle includes inserting the second end of the inlet tubethrough the region adjacent the juncture of the pulmonary veins andadvancing the inlet tube whereby the second end passes through themitral valve the and into the left ventricle.
 6. The method according toclaim 2 wherein the step of accessing the left ventricle includesinserting the second end of the inlet tube within the aorta andadvancing the inlet tube through the aortic valve such that the secondend is disposed in the left ventricle.
 7. The method according to claim6 wherein the step of accessing the aorta includes inserting the secondend of the outlet tube within the descending aorta.
 8. The methodaccording to claim 7 further including the step of occluding the aortaof the patient adjacent the heart to isolate the left ventricle.
 9. Themethod according to claim 8 including the step of introducing acardioplegia solution into the left ventricle.
 10. A method forproviding at least partial bypass of the heart by supporting the leftside of the heart to thereby enable the surgeon to perform varioussurgical procedures thereon, the heart having a left atrium forreceiving oxygenated blood from the lungs and a left ventricle forpumping the oxygenated blood through the aorta to the systemic arteries,and a right atrium for receiving oxygen-depleted blood from the systemicveins and a right ventricle for directing the oxygen-depleted bloodthrough the pulmonary artery and into the lungs for oxygenation, themethod comprising the steps of: providing a circulatory assist systemincluding a portable extracorporeal axial flow pump having a pumphousing defining a longitudinal axis, the pump housing having an inletport and an outlet port, a rotating pumping member disposed in the pumphousing, an inlet tube having a first end connected to the inlet portand a second end for contact with the body, an outlet tube having afirst end connected to the outlet port and a second end for contact withthe body, each tube having an axial lumen between the first and secondends defining a blood flow path for conveyance of blood therealong;accessing the patient's left atrium of the heart with the inlet tubesuch that the second end of the inlet tube is in fluid communicationwith the left atrium; accessing the aorta with the outlet tube such thatthe second end of the outlet tube is in fluid communication with theaorta; actuating the rotating pumping member to draw oxygenated bloodfrom the left atrium of the heart through the second end of the inlettube and through the axial lumen of the inlet tube and into the inletport of the pump housing whereby the pumping member imparts mechanicalenergy to the oxygenated blood passing through the pump housing anddirects the oxygenated blood through the outlet port and through theaxial lumen of the outlet tube and the second end of the outlet tube tobe transferred by the aorta to the systemic arteries; and permitting theright side of the heart to function whereby oxygen-depleted bloodreturning through the systemic veins to the right atrium is directedthrough the right ventricle to the patient's lungs for oxygenation andsubsequent pulmonary circulation.
 11. The method according to claim 10further including the step of positioning the extracorporeal portablepump either on the patient's body or directly adjacent the patient'sbody.
 12. The method according to claim 11 wherein the step of accessingthe left atrium of the heart includes inserting the second end of theinlet tube through a heart wall portion adjacent the left atrium suchthat the second end is disposed in the left atrium.
 13. The methodaccording to claim 10 wherein the step of accessing the left atrium ofthe heart includes inserting the second end of the inlet tube throughthe region adjacent the juncture of the pulmonary veins and advancingthe inlet tube whereby the second end is disposed in the left atrium.14. The method according to claim 10 wherein the step of accessing theaorta comprises inserting the second end of the outflow tube through theaorta wall.
 15. A method for providing at least partial bypass of theheart by supporting the heart to thereby enable the surgeon to performvarious surgical procedures thereon, the heart having a left atrium forreceiving oxygenated blood from the lungs and a left ventricle forpumping the oxygenated blood through the aorta to the systemic arteries,and a right atrium for receiving oxygen-depleted blood from the systemicveins and a right ventricle for directing the oxygen-depleted bloodthrough the pulmonary artery and into the lungs for oxygenation, themethod comprising the steps of: supporting the pumping function of theleft side of the heart by; providing a circulatory assist systemincluding-.a portable extracorporeal axial flow pump having a pumphousing defining a longitudinal axis, the pump housing having an inletport and an outlet port, the outlet port being in substantial axialalignment with the inlet port, a rotating pumping member disposed in thepump housing, an inlet tube having a first end connected to the inletport and a second end for contact with the body, an outlet tube having afirst end connected to the outlet port and a second end for contact withthe body, each tube having an axial lumen between the first and secondends defining a blood flow path for conveyance of blood therealong;accessing the patient's left atrium of the heart with the inlet tubesuch that the second end of the inlet tube is in fluid communicationwith the left atrium; accessing the aorta with the outlet tube such thatthe second end of the outlet tube is in fluid communication with theaorta; actuating the rotating pumping member to draw oxygenated bloodfrom the left atrium of the heart through the second end of the inlettube and through the axial lumen of the inlet tube and into the inletport of the pump housing whereby the pumping member imparts mechanicalenergy to the oxygenated blood passing through the pump housing anddirects the oxygenated blood through the outlet port and through theaxial lumen of the outlet tube and the second end of the outlet tube tobe transferred by the aorta to the systemic arteries; and supporting thepumping function of the right side of the heart while permitting thepatient's lungs to function in oxygenating the blood.
 16. The methodaccording to claim 15 wherein the step of supplementing the pumpingfunction of the right side of the heart includes: providing a secondcirculatory assist system including a portable extracorporeal axial flowpump having a pump housing defining a longitudinal axis, the pumphousing having an inlet port and an outlet port, the outlet port beingin substantial axial alignment with the inlet port, a rotating pumpingmember disposed in the pump housing, an inlet tube having a first endconnected to the inlet port and a second end for contact with the body,an outlet tube having a first end connected to the outlet port and asecond end for contact with the body, each tube having an axial lumenbetween the first and second ends defining a blood flow path forconveyance of blood therealong; accessing the patient's right atrium orthe right ventricle of the heart with the inlet tube such that thesecond end of the inlet tube is in fluid communication with the rightatrium or the right ventricle; accessing the aorta with the outlet tubesuch that the second end of the outlet tube is in fluid communicationwith the aorta; actuating the rotating pumping member to draw oxygenatedblood from the right atrium or the right ventricle of the heart throughthe second end of the inlet tube and through the axial lumen of theinlet tube and into the inlet port of the pump housing whereby thepumping member imparts mechanical energy to the oxygenated blood passingthrough the pump housing and directs the oxygenated blood through theoutlet port and through the axial lumen of the outlet tube and thesecond end of the outlet tube to be transferred by the pulmonary arteryto the lungs for oxygenation.
 17. A circulatory support device, whichcomprises: a pump housing including an inlet end portion defining aninlet port for permitting blood to enter the pump housing and an outletend portion defining an outlet port for permitting blood to exit thepump housing, the inlet and outlet end portions each having central hubportions with straightener blades extending therefrom for facilitatingpassage of blood through the pump housing; a rotatable member mountedfor rotational movement to the central hub portions of the pump housing,the rotatable member including at least one impeller blade for impartingpump energy to blood passing through the pump housing, the rotatablemember having a magnetically actuated rotor; and a motor stator disposedin the pump housing, the motor stator and the rotatable member having anannular space therebetween defining a blood path for blood to flowthrough the pump housing, the motor stator having at least one statorblade extending from an inner surface thereof, the one stator blade andthe one impeller blade of the rotatable member cooperatively configuredto exert a substantially axial flow pumping energy to blood flowingalong the blood path.
 18. The device according to claim 17 wherein theone impeller blade extends axially and peripherally with respect to alongitudinal axis of the pump housing.
 19. The device according to claim18 wherein the one stator blade extends axially and peripherally withrespect to the longitudinal axis.
 20. The device according to claim 19including a plurality of impeller blades and a plurality of statorblades.
 21. The device according to claim 19 wherein the one statorblade is disposed between the one impeller blade and the outlet endportion of the pump housing.
 22. The device according to claim 17including an inflow tube connected to the inlet end portion of the pumphousing and configured for accessing one of a major blood vessel and theheart of a patient.
 23. The device according to claim 22 furtherincluding an outflow tube connected to the outlet end portion of thepump housing for accessing one of a major blood vessel and the heart ofa patient.
 24. A method for providing at least partial bypass of theheart to supplement the pumping function of the heart to thereby enablethe surgeon to perform various surgical procedures thereon, the hearthaving a left atrium for receiving oxygenated blood from the lungs and aleft ventricle for pumping the oxygenated blood through the aorta to thesystemic arteries, and a right atrium for receiving oxygen-depletedblood from the systemic veins and a right ventricle for pumping theoxygen-depleted blood through the pulmonary artery and into the lungsfor oxygenation, the method comprising the steps of: supplementing thepumping function of the left side of the heart by; providing acirculatory assist system including a portable extracorporeal axial flowpump having a pump housing defining a longitudinal axis, the pumphousing having an inlet port and an outlet port, the outlet port beingin substantial axial alignment with the inlet port, a rotating pumpingmember disposed in the pump housing, an inlet tube having a first endconnected to the inlet port and a second end for contact with the body,an outlet tube having a first end connected to the outlet port and asecond end for contact with the body, each tube having an axial lumenbetween the first and second ends defining a blood flow path forconveyance of blood therealong; accessing the left ventricle of theheart with the inlet tube such that the second end of the inlet tube isin fluid communication with the left ventricle; accessing the aorta withthe outlet tube such that -the second end of the outlet tube is in fluidcommunication with the aorta; actuating the rotating pumping member todraw oxygenated blood from the left ventricle of the heart through thesecond end of the inlet tube and through the axial lumen of the inlettube and into the inlet port of the pump housing whereby the pumpingmember imparts mechanical energy to the oxygenated blood passing throughthe pump housing and directs the oxygenated blood through the outletport and through the axial lumen of the outlet tube and the second endof the outlet tube to be transferred by the aorta to the systemicarteries; and supplementing the pumping function of the right side ofthe heart while permitting the patient's lungs to function inoxygenating the blood.
 25. The method according to claim 24 wherein thestep of supplementing the pumping function of the right side of theheart includes: providing a second circulatory assist system including aportable extracorporeal axial flow pump having a pump housing defining alongitudinal axis, the pump housing having an inlet port and an outletport, the outlet port being in substantial axial alignment with theinlet port, a rotating pumping member disposed in the pump housing, aninlet tube having a first end connected to the inlet port and a secondend for contact with the body, an outlet tube having a first endconnected to the outlet port and a second end for contact with the body,each tube having an axial lumen between the first and second endsdefining a blood flow path for conveyance of blood therealong; accessingthe right atrium or the right ventricle of the heart with the inlet tubesuch that the second end of the inlet tube is in fluid communicationwith the right atrium or the right ventricle; accessing the pulmonaryartery with the outlet tube such that the second end of the outlet tubeis in fluid communication with the pulmonary artery; actuating therotating pumping member to draw oxygen-depleted blood from the rightatrium or the right ventricle of the heart through the second end of theinlet tube and through the axial lumen of the inlet tube and into theinlet port of the pump housing whereby the pumping member impartsmechanical energy to the oxygen-depleted blood passing through the pumphousing and directs the oxygen-depleted blood through the outlet portand through the axial lumen of the outlet tube and the second end of theoutlet tube to be transferred by the pulmonary artery to the lungs foroxygenation.
 26. A circulatory support system to supplement ortemporarily replace the pumping function of a patient's heart to therebyenable a surgeon to perform surgical procedures thereon, comprising: anextracorporeal portable blood flow pump having inlet and outlet ports, arotating member rotatably mounted in the pump housing to impartmechanical energy to blood entering the inlet port and to direct theblood through the outlet port; an inlet cannula connected to the inletport of the pump housing and having an inlet open end portiondimensioned for insertion within the patient's heart or blood vesselassociated with the heart so that blood is drawn from the patientthrough a lumen of the inlet cannula and directed into the pump housing;an outlet cannula connected to the outlet port of the pump housing andhaving an outlet end portion dimensioned for insertion within thepatient so that blood exiting the outlet port of the pump housing isconveyed through a lumen of the outlet tube into the patient fortransfer by the arterial system of the patient; a control unit having aprocessor, operatively coupled to the flow pump, for controllingoperation thereof; an air bubble sensor mounted to one of the cannulasfor detecting air bubbles in the respective cannula and providing abubble detect signal indicative of the presence of an air bubble; aclamping device mounted to one of the cannulas and operative to clampdown on the respective cannula when the bubble detect signal isgenerated to prevent air from entering the patient's bloodstream;wherein the control unit is operative, responsive to receiving thebubble detect signal, to generate an air bubble alarm and to causerotation of the rotating member of the pump to cease.
 27. The system ofclaim 26 wherein the air bubble sensor is mounted to the inlet cannulaand the clamping device is mounted to the outlet cannula.
 28. The systemof claim 26, wherein the control unit includes a manual switch to permitthe pump to be restarted following activation of the bubble alarm, thecontrol unit being responsive to manual operation of the switch toextinguish the bubble alarm and restart rotation of the rotating member.29. The system of claim 26, further including a flow sensor coupled toone of the inlet or outlet cannulas and providing a flow sense signal tothe control unit indicative of blood flow rate within the respectivecannula, the control unit operative to generate a low flow rate alarmwhen the flow rate is determined to be below a predetermined threshold.30. The system of claim 29 wherein, subsequent to the generation of thelow flow rate alarm, the control unit is operative to extinguish the lowflow rate alarm when the flow rate is determined to have risen above apredefined threshold.
 31. The system of claim 26, further including apressure transducer for sensing pressure on the inlet side of the pumpand providing a pressure sense signal indicative of the pressure sensed,the control unit being operable to command a reduction in motor speed toa non-zero signal when the pressure is determined to be below apredetermined threshold.
 32. The system of claim 31 wherein saidpressure transducer is disposed in proximity to the inlet open endportion of the inlet cannula, and the system further including a wirerunning within an outer sheathing of the inlet cannula from the controlunit to the pressure transducer, the pressure sense signal beingtransmitted to the control unit on the wire.
 33. The system of claim 31,wherein, following the reduction in motor speed, the control unit isoperative to ramp up the motor speed to a speed corresponding to amanually set dial, following a determination based on the pressure sensesignal that the pressure has risen to a value above a predefinedthreshold for at least a specified period of time.
 34. The system ofclaim 26 wherein the control unit includes circuitry for sensing motorcurrent and for generating an alarm when the motor current has risenabove a predetermined threshold.
 35. The system of claim 26 wherein theaxial flow pump includes a pump housing dimensioned for positioningdirectly on or adjacent to the chest area of a patient.
 36. The systemof claim 26 wherein the control unit includes a backup motor controllercircuit and a manual engage backup switch, the control unit entering abackup mode upon activation of the engage backup switch, the controlunit operative in the backup mode to control motor speed based on manualmotor speed control independent of alarm conditions.
 37. A control unitfor use in a circulatory support system to supplement or temporarilyreplace the pumping function of a patient's heart, the support systemincluding a blood flow pump, inlet and outlet cannulas coupled to theflow pump for insertion within the patient, an air bubble detector, anda cannula clamp, each coupled to one of the cannulas, the control unitcomprising: circuitry for supplying power to the flow pump to cause thepump to rotate; circuitry responsive to a bubble sense signal providedby the bubble detector, for generating a bubble alarm and for causingrotation of the pump to cease if the bubble sense signal indicates thepresence of an air bubble; and circuitry responsive to the bubble sensesignal indicating the presence of an air bubble for causing the cannulaclamp to clamp down on the respective cannula to prevent air fromentering the patient's bloodstream.
 38. The control unit of claim 37,further comprising a manual switch to permit the pump to be restartedfollowing activation of the bubble alarm, the control unit beingresponsive to manual operation of the switch to extinguish the bubblealarm, restart the pump and cease actuation of the cannula clamp. 39.The control unit of claim 38, wherein the system further includes apressure transducer coupled to the inlet cannula and a flow rate sensorcoupled to one of the cannulas, the control unit operative to receive apressure sense signal from the pressure transducer and to command areduction in motor speed to a non-zero speed and generate a low pressurealarm when the pressure is determined to be below a predeterminedpressure threshold, and to generate a low flow rate alarm when the flowrate is determined to be below a predetermined flow threshold based on aflow rate signal received from the flow sensor.
 40. The control unit ofclaim 39, wherein, following the reduction in motor speed, the controlunit is operative to ramp up the motor speed to a speed corresponding toa manually set dial, following a determination based on the pressuresense signal that the pressure has risen to a value above a predefinedthreshold for at least a specified period of time.
 41. The control unitof claim 40, further including circuitry for sensing motor current andfor generating an alarm when the motor current has risen above apredetermined threshold.
 42. The control unit of claim 37, furtherincluding a backup motor controller circuit and a manual engage backupswitch, the control unit entering a backup mode upon activation of theengage backup switch, the control unit operative in the backup mode tocontrol motor speed based on manual motor speed control independent ofalarm conditions.
 43. The control unit of claim 37, having a housing ofa generally long, solid rectangular shape to facilitate use within anoperating room.
 44. The control unit of claim 43 wherein the controlunit housing is about four feet in height, about one foot in width andseveral inches in thickness.
 45. The control unit of claim 37, furtherincluding: a front portion with a front display that displays motorspeed and flow rate and visible alarm indicators corresponding toparticular alarm conditions; and a rear portion with a rear display thatdisplays motor speed and flow rate and generally the same visible alarmindicators as the front display.
 46. The control unit of claim 37,further including circuitry for receiving a flow rate signal from a flowrate sensor coupled to one of the cannulas, means for generating,responsive to the flow rate signal, a low flow rate alarm if flow rateis determined to be below a predetermined threshold, and a flow blockagealarm if the flow rate has dropped by more than a predefined amount orpercent.
 47. A circulatory support system to supplement or temporarilyreplace the pumping function of a patient's heart to thereby enable asurgeon to perform surgical procedures thereon, comprising: anextracorporeal portable blood flow pump having inlet and outlet ports, arotating member rotatably mounted in the pump housing to impartmechanical energy to blood entering the inlet port and to direct theblood through the outlet port; an inlet cannula connected to the inletport of the pump housing and having an inlet open end portiondimensioned for insertion within the patient's heart or blood vesselassociated with the heart so that blood is drawn from the patientthrough a lumen of the inlet cannula and directed into the pump housing;an outlet cannula connected to the outlet port of the pump housing andhaving an outlet end portion dimensioned for insertion within thepatient so that blood exiting the outlet port of the pump housing isconveyed through a lumen of the outlet tube into the patient fortransfer by the arterial system of the patient; a control unit having aprocessor, operatively coupled to the flow pump, for controllingoperation thereof; and a pressure transducer for sensing pressure on theinlet side of the pump and providing a pressure sense signal indicativeof the pressure sensed to the control unit, the control unit beingoperable to command a reduction in motor speed to a lower speed when thepressure is determined to be below a predetermined threshold.
 48. Thesystem of claim 47 wherein said pressure transducer is disposed inproximity to the inlet open end portion of the inlet cannula, and thesystem further including a wire running within an outer sheathing of theinlet cannula from the control unit to the pressure transducer, thepressure sense signal being transmitted to the control unit on the wire.49. The system of claim 47 wherein the reduction in motor speed to alower speed is repeated such that the motor speed is ramped down, untilthe pressure is determined to have risen to a value above a predefinedthreshold, and the control unit being operative to ramp up the motorspeed if the pressure has risen above the predefined threshold.
 50. Thesystem of claim 47, further including an air bubble sensor mounted toone of the cannulas for detecting air bubbles in the respective cannulaand providing a bubble detect signal indicative of the presence of anair bubble; wherein the control unit is operative, responsive toreceiving a bubble detect signal, to generate an air bubble alarm and tocause rotation of the rotating member of the pump to cease.
 51. Acontrol unit for use in a circulatory support system to supplement ortemporarily replace the pumping function of a patient's heart, thesupport system including a blood flow pump, inlet and outlet cannulascoupled to the flow pump for insertion within the patient, and apressure transducer coupled to the inlet cannula, the control unitcomprising: circuitry for supplying power to the flow pump to cause thepump to rotate at a first speed; and circuitry responsive to a pressuresense signal from the pressure transducer, the control unit beingoperable to command a reduction in motor speed to a lower motor speedwhen the pressure is determined to be below a predetermined threshold.52. The control unit of claim 51 wherein the reduction in motor speed toa lower speed is repeated such that the motor speed is ramped down,until the pressure is determined to have risen to a value above apredefined threshold, and the control unit being operative to ramp upthe motor speed if the pressure has risen above the predefinedthreshold.
 53. The control unit of claim 52, wherein the motor speed ismaintained at a reduced motor speed once it is determined that thepressure has risen above the predefined threshold, and the motor speedbeing ramped up only after it is determined that the pressure has beenabove the predefined threshold for a specified period of time.
 54. Thecontrol unit of claim 51, further including circuit means, responsive toa bubble detect signal from an air bubble detector indicative of thepresence of an air bubble in one of the cannulas, for generating an airbubble alarm and causing rotation of the rotating member of the pump tocease.
 55. The system of claim 26 wherein said blood flow pump comprisesan axial blood flow pump.
 56. The control unit of claim 37 wherein saidblood flow pump comprises an axial flood flow pump.
 57. The system ofclaim 47 wherein said blood flow pump comprises an axial blood flowpump.
 58. The control unit of claim 51 wherein said blood flow pumpcomprises an axial flood flow pump.